ABSTRACT Support is requested for a Keystone Symposia conference entitled Mononuclear Phagocytes in Health, Immune Defense and Disease, organized by Drs. Steffen Jung and Miriam Merad. The conference will be held in Austin, Texas from April 30 ? May 4, 2017. Mononuclear phagocytes (MNP) are immune cells that are uniquely equipped to sense and respond to environmental cues by promoting tissue homeostasis or initiating tissue repair and immunity. MNP also contribute significantly to tissue pathologies, and their manipulation holds considerable therapeutic potential. MNP display major functional specializations. Most macrophages are established before birth and perform tissue-specific functions in organ development and homeostasis. Short-lived classical dendritic cells (DC) are specialized in triggering adaptive T cell immunity. Monocytes complement macrophages and DC as highly plastic cells, in particular during inflammation. While MNP subsets have been identified, individual contributions to health and disease are not well-defined. Breathtaking technological advance in genomic profiling of populations and single cells is revealing the breadth of MNP functions and identifying molecular checkpoints for targeted therapeutic intervention. These molecular efforts are paralleled by astounding progress in imaging capabilities, enabling the study of the cells in their physiological context. This conference therefore aims to: 1) Cover recent progress in the field, revealing novel and differential contributions of MNP in physiological processes, and identify critical knowledge gaps; 2) Stimulate scientific exchange, in particular between clinicians and researchers, to better translate findings from animal models into human settings and brainstorm regarding novel therapeutic intervention; and 3) Develop novel conceptual frameworks for future studies of MNP in health and disease.